Prostheses for implantation in blood vessels or other similar organs of the living body are, in general, well known in the medical art. For example, prosthetic endovascular grafts constructed of biocompatible materials have been employed to replace or bypass damaged or occluded natural blood vessels. In general, endovascular grafts include a graft anchoring component that operates to hold a tubular graft component of a suitable graft material in its intended position within the blood vessel. Most commonly, the graft anchoring component is one or more radially compressible stents that are radially expanded in situ to anchor the tubular graft component to the wall of a blood vessel or anatomical conduit. Thus, endovascular grafts are typically held in place by mechanical engagement and friction due to the opposition forces provided by the radially expanded stents.
Grafting procedures are also known for treating aneurysms. Aneurysms result from weak, thinned blood vessel walls that “balloon” or expand due to aging, disease and/or blood pressure in the vessel. Consequently, aneurysmal vessels have a potential to rupture, causing internal bleeding and potentially life threatening conditions. Grafts are often used to isolate aneurysms or other blood vessel abnormalities from normal blood pressure, reducing pressure on the weakened vessel wall and reducing the chance of vessel rupture. As such, a tubular endovascular graft may be placed within the aneurysmal blood vessel to create a new flow path and an artificial flow conduit through the aneurysm, thereby reducing if not nearly eliminating the exertion of blood pressure on the aneurysm.
In general, rather than performing an open surgical procedure to implant a bypass graft that may be traumatic and invasive, endovascular grafts which may be referred to as stent-grafts are preferably deployed through a less invasive intraluminal delivery procedure. More particularly, a lumen or vasculature is accessed percutaneously at a convenient and less traumatic entry point, and the stent-graft is routed through the vasculature to the site where the prosthesis is to be deployed. Intraluminal deployment is typically effected using a delivery catheter with coaxial inner and outer tubes or shafts arranged for relative axial movement. For example, a self-expanding stent-graft may be compressed and disposed within a distal end of an outer shaft or sheath component of the delivery catheter distal of a stop fixed to an inner shaft or member. The delivery catheter is then maneuvered, typically tracked through a body lumen until a distal end of the delivery catheter and the stent-graft are positioned at the intended treatment site. The stop on the inner member is then held stationary while the sheath component of the delivery catheter is withdrawn. The stop on the inner member prevents the stent-graft from being withdrawn with the sheath component. As the sheath component is withdrawn, the stent-graft is released from the confines thereof and radially self-expands so that at least a portion of it contacts and substantially conforms to a portion of the surrounding interior of the lumen, e.g., the blood vessel wall or anatomical conduit.
In recent years, to improve optimal control and alignment during deployment and positioning of a stent-graft, various tip capture mechanisms have been incorporated into the delivery system used for percutaneously delivering the prosthesis. Tip capture involves restraining a proximal end stent of the stent-graft in conjunction with a main body restraint achieved by other delivery system components, such as a tubular outer shaft or sheath component. The tip capture mechanism can be activated at any time during stent-graft deployment to suit any number of system characteristics driven by the therapy type, stent-graft type, or specific anatomical conditions that may prescribe the release timing. Typically, the tip capture release is activated after some or all of the main stent-graft body release, and thus provides a means of restraining the stent-graft during positioning. Additional restraint of the stent-graft is a key characteristic when the operator is attempting to accurately position the stent relative to an anatomical target.
For example, U.S. Patent Application Publication No. 2006/0276872 to Arbefuielle et al. and U.S. Patent Application Publication No. 2009/0276207 to Glynn et al., both herein incorporated by reference in their entirety, describe tip capture mechanisms that restrain a proximal end stent of the stent-graft while the remainder of the stent-graft expands, then releases the proximal end stent. The proximal end stent is attached to the graft material of the stent-graft so as to have an “open web” or “free flow” proximal end configuration in which the endmost crowns thereof extend past or beyond the graft material such that the endmost crowns are exposed or bare, and thus free to interact with a tip capture mechanism and couple the prosthesis to the delivery system. The open web proximal end configuration allows blood flow through the endmost crowns for perfusion during and/or after implantation. FIGS. 1A and 1B illustrate a delivery system 10 having a tip capture mechanism 12 designed to couple or interact with a stent-graft 14 having an open web or free flow proximal end configuration 16. More particularly, endmost crowns 18 of a proximal end stent 15 engage or extend around retractable finger or prong-like elements 20 of the tip capture mechanism. When an outer delivery shaft 22 is retracted to allow stent-graft 14 to self-expand, endmost crowns 18 of the proximal end stent 15 remain engaged around tip capture fingers 20, as shown in FIG. 1A. To release proximal end stent 15, a shaft 24 coupled to finger or prong-like elements 20 is refracted and end stent 15 is allowed to self-expand, as shown in FIG. 1B. The Captivia Delivery System manufactured by Medtronic Vascular, Inc. of Santa Rosa, Calif. is one example of a delivery system having a tip capture mechanism as described above, which may be used for delivering endovascular stent-grafts such as the Valiant Thoracic Stent-graft manufactured by Medtronic Vascular, Inc. of Santa Rosa, Calif.
Tip capture mechanisms have improved accuracy of deployment of self-expanding stent-grafts having open web or free flow configurations. However, in some cases a closed web configuration may be required or chosen due to application and/or user preferences. In a closed web configuration, the endmost crowns do not extend past or beyond the graft material but rather are covered or lined by graft material. For example, a stent-graft having a closed web configuration may be selected to treat dissections or vessel transections due to the related condition of the vessel tissue. In these cases, the tissue is fragile and may be damaged by exposed stent struts or apices. A closed web stent-graft thus presents a proximal configuration that is less traumatic to sensitive tissues or disease states. However, stent-grafts having a closed web proximal configuration do not have a bare proximal end stent free to interact with a tip capture mechanism of a delivery system, and thus may present challenges during deployment with varied success of achieving control during delivery without using tip capture. Embodiments hereof relate to a stent-graft having a closed web proximal end configuration that may interact with a tip capture mechanism of a delivery system.